1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device capable of automatically switching to a transmission mode or a reflection mode, and a method for driving the same.
2. Discussion of the Related Art
The cathode ray tube (CRT) is widely used as a display device. While cathode ray tube based displays are commonly used as the monitors for information terminal apparatuses, because of their size and weight, CRT based displays are not well suited to address the current trends for miniaturization and lightweight trends for electronic products.
Displays using liquid crystal display (LCD) devices have advantages of light weight, low power consumption, and slim profile when compared to CRT displays. In particular, displays employing LCD devices using thin film transistors (TFTs) having high image quality, large sizes, and color display capability nearly equal to that of a CRT are widely used in a variety of applications including monitors and the displays of notebook personal computers (PCs).
The LCD device is a transmissive display device and controls an amount of light passing through a liquid crystal (LC) layer using anisotropy in a refractive index of LC molecules contained in the LC layer to display a desired image on a screen. A typical LCD device may include a backlight unit to provide light for transmitting through the LC layer in order to display pixels of an image. Such a LCD device can be roughly divided into an LC display panel and a backlight unit provided at the rear of the LC display panel.
The LC display panel is the portion of an LCD device on which the image is realized and includes a lower substrate, an upper substrate, and an LC layer interposed between the two substrates. The lower substrate includes a driving device such as a TFT and a pixel electrode. The upper substrate includes a color filter layer and a common electrode. A driving circuit unit is provided on a lateral side of the lower substrate to apply signals to the TFT, the pixel electrode, and the common electrode formed on the lower substrate, respectively.
The backlight unit includes a light source for emitting light, a reflector for reflecting light generated from the light source to improve a light efficiency, and optical sheets for diffusing and condensing the light.
LCD devices are roughly classified into transmission type LCD devices displaying an image using light incident from a backlight unit, and reflection type LCD devices displaying an image by reflecting external light such as natural light. The transmission type LCD device has the disadvantage that power consumption of the backlight unit is large. Meanwhile, the reflection type LCD device has the disadvantage that an image cannot be displayed in dark environments because the reflection type LCD device depends on ambient light to display images.
To address these problems, a transflective LCD device has been developed which can selectively operate in either a transmission mode using a backlight unit or in a reflection mode using external light. Because the transflective LCD device operates in a reflection mode when ambient light is sufficient and operates in a transmission mode using a backlight unit when the ambient light is not sufficient, transflective LCD devices may have reduced power consumption compared to the transmission type LCD device and are not limited by external light conditions as is the reflection type LCD device.
In a related art transflective LCD device, a user judges the amount of ambient light and selects a reflection mode or a transmission mode. Therefore, the transflective LCD device may be operated in the reflection mode when the amount of ambient light is not sufficient, and may be operated in the transmission mode when the amount of ambient light is sufficient. With a transflective LCD device in which the mode is selected by a user, the user may not accurately judge the amount of external light and light from the backlight unit. Accordingly the user may select the reflection mode even when the amount of ambient is not sufficient for proper viewing of the display, or may select the transmission mode even though there is a sufficient amount of ambient external light is sufficient for producing a quality display without reducing the display quality of the transflective LCD device.